Legal regulations stipulate the monitoring of the composition of the exhaust gas of internal combustion engines to maintain limiting values. For this purpose, undesirable substances, such as nitrogen oxides and carbon monoxide, in the exhaust gas are converted into substances considered to be noncritical, such as water vapor, carbon dioxide, and nitrogen, with the aid of controlled three-way catalytic converters. This conversion presumes that the fuel-air mixture supplied to the internal combustion engine is in a certain composition range close to a stoichiometric composition. It is designated by parameter λ=1. The composition of the fuel-air mixture is monitored using exhaust gas sensors provided in the exhaust gas duct of the internal combustion engine, for example, in the form of broadband lambda sensors, which determine the oxygen partial pressure.
The correct function of the exhaust gas sensors and in particular also their aging resistance is strongly dependent on their electronic circuit. The lambda regulation has particular significance in this case, the exhaust gas sensors available on the market being able to have different characteristics with respect to the dynamic response and the dead times. To be able to ensure a stable regulation, for example, lambda controllers installed in engine control units have to be supplemented using additional electronic circuits, if exhaust gas sensors, in particular from different suppliers, are installed. For this purpose, for example, a lambda controller known as a “CJ135 Lambda Probe Interface IC” is used, which contains a PID controller.
Calibration and diagnostic measurements usually result in short-term signal invalidity during the operation and the evaluation of lambda sensors, since the control system is typically brought out of equilibrium. Depending on the length of the signal invalidity, violations of the law may occur with respect to monitoring and emissions. To avoid this, some lambda sensor diagnostic measurements are placed in the coasting or start-stop phases of the internal combustion engine, which is often not desired by the automobile manufacturers. The CJ135 lambda controller intrinsically already offers the capability of having calibration measurements run in parallel to the pump current operation, without influencing it. However, such diagnostic measurements usually still result in temporary invalidity of the signal when they are carried out in parallel with the pump current operation.